Sarepta faces another FDA delay with its much-scrutinized DMD drug

Sarepta Therapeutics ($SRPT), hoping to win approval with a treatment for Duchenne muscular dystrophy, will have to endure a three-month FDA delay before getting the final word on its drug.

The agency has prolonged its review of Sarepta's eteplirsen, which is designed to address the genetic defect that causes some cases of DMD, and promised to weigh in on the drug by May 26. The FDA had initially planned to hand down a final decision by Feb. 26, but the weather-related postponement of a key hearing last month disrupted the schedule.

The delay also gives the agency more time to review some new data Sarepta submitted last month, the company said, which includes four years of clinical results showing how well DMD patients treated with eteplirsen can walk compared with historical data. The company believes those additional results will bolster its case for approval.

But the FDA's last public take on eteplirsen suggests that'll be an uphill effort. In documents released ahead of last month's now-delayed panel meeting, agency staff picked apart Sarepta's supporting data and questioned whether the drug works at all.

The company is seeking approval based largely on a small study with no placebo control, comparing eteplirsen's results against historical data in the muscle-wasting disease. But regulators took serious issue with Sarepta's thesis, pointing out flaws in the study design and raising questions over whether eteplirsen's intermittent efficacy might be attributable to something else entirely.

"Although FDA is prepared to be flexible with respect to a devastating illness with no treatment options, we cannot approve drugs for which substantial evidence of effectiveness has not been established," FDA reviewers wrote.

Sarepta will get the chance to make its case at a future meeting of independent FDA advisers, which has yet to be rescheduled after January's snowstorm.

A similar drug from BioMarin ($BMRN), drisapersen, got rejected by the FDA last month over efficacy concerns of its own. Both drugs aim to treat DMD through a process called exon skipping, forcing the body to ignore the genetic defect that results in faulty dystrophin production and leads to about 13% of disease cases.